Method for treating diamonds to produce bondable diamonds for depositing same on a substrate

ABSTRACT

A metastable crystal layer is deposited by chemical plasma deposition on diamonds at subatmospheric pressure (10 -3  Torr) at 850°-1050° C. The metastable layer enables the diamond to be metallurgically bonded to a suitable substrate.

This is a continuation of copending application Ser. No. 07/605,080,filed on Oct. 29, 1990, now U.S. Pat. No. 5,164,220.

BACKGROUND OF THE INVENTION

The present invention relates to the bonding of diamonds to suitablesubstrates, and more particularly, to the treatment of the diamonds tometallurgically bond the diamonds to the substrate.

This invention relates to a process for growing of a metastable crystallayer over diamonds, silicon carbide, or cubic boron nitride by chemicalplasma deposition under subatmospheric pressure and relatively lowtemperature. This can produce a metallurgical bond when mixed withsuitable metal powder at its liquid or eutectic temperature and highpressure. It is also possible to produce a metallurgical bond in anaqueous solution having a heterogeneous catalyst, if used with squarewave pulse current.

Several processes are disclosed in the patents and literature mentionedin the references but all use the growth of diamonds with the object ofproducing synthetic diamonds, departing from a diamond seed. Obviously,the principal disadvantage of all of these processes is in terms ofeconomical considerations, at least until now.

Hibshman, U.S. Pat. No. 3,371,996, Angus et al, U.S. Pat. No. 3,661,526,and Vickery, U.S. Pat. No. 3,714,334, disclose processes for growingdiamonds by facilitating or catalyzing a reaction between hydrogen and ahydrocarbon to form crystal carbon. Hibshman discloses a catalyticdiamond growth process in which a solid, particulate catalytic metal ismixed with finely divided diamond seed and contacted with CO gas at apressure of 1 atm-2000 atm and temperature of 600° C. to 1100° C.

Angus et al deposits a layer of a catalytic metal on the diamond seedsurface and passes methane gas over the diamond at pressures of 10⁻⁸-759 Torr and temperatures of 800° to 700° C. The catalyst acts as acatalytic mobile transfer medium which aids in promoting the transitionof carbon in the form of a precursor in the vapor phase to themetastable diamond in the solid phase. Angus further states that thecatalytic mobile transfer medium may contain materials, such as nickel,which will inhibit the formation of elemental carbons (carbides).

Strong, U.S. Pat. No. 2,947,609, discloses a process for formingdiamonds under high pressure (5000 to 115000 atm) and high temperature(1200° C. to 2600° C.) in the presence of a catalyst. Strong disclosesthat diamond forms at the interface of the catalyst alloy andcarbonaceous material.

Caveney, U.S. Pat. No. 3,879,901, Vereschagin et al, U.S. Pat. No.3,912,500, and Bakul et al, U.S. Pat. No. 4,097,274, disclose processesfor producing diamond compacts. They compress diamond powder and ametallic binder under high pressure and temperature forming a diamondmatrix which is filled and held together with the metallic binder.

St. Pierre et al, U.S. Pat. No. 4,220,455, Lee et al, U.S. Pat. No.4,234,661, and Morelock, U.S. Pat. No. 4,247,304, disclose a process forforming a diamond compact by infiltrating a mass of diamonds coated withelemental non-diamond carbon with fluid silicon. The silicon reacts withnon-diamond carbon to bind the diamonds together by a bonding medium ofsilicon carbide and elemental silicon. These patents disclose that thebody may be formed on a substrate and that the liquid silicon, duringinfiltration, may penetrate the substrate to bond the diamond body orcompact to the substrate.

These patents disclose processes for growing diamond crystals andcreating diamond compacts. None disclose treating a diamond to enablethe treated diamonds to bond to a suitable metal powder, or a thedeposition of a metal and the treated diamond on a substrate byelectrolytic or chemical plasma deposition.

One object of the invention is to provide a novel method for producingbondable diamonds, silicon carbide or cubic boron nitride.

Another object is to provide a container in which to produce suchbondable diamonds.

Another object is to provide such a bondable diamond which will bondwith a suitable substrate.

Another object is to provide such a bondable diamond which may be usedfor manufacturing cutting tools.

Another object is to provide such a bondable crystal which may be usedfor manufacturing a rotary cutting tool by electroplating but in thepresence of a catalyst.

Other objects inherent in this invention will be better understood byreference to the description and examples.

SUMMARY OF THE INVENTION

In accordance with this invention, generally stated, it is possible togrow an epitaxial metastable crystal layer on diamonds as well as SiC orcubic boron nitride CBN, by placing the crystals in contact with asuitable silane in an environment consisting of 96% H₂ by volume and nomore than 4% of the silane. The diamond is treated at a temperature inthe range of about 800° C. to about 1050° C., at a subatmosphericpressure of 1×10⁻³ Torr, in the presence of a catalyst selected from theplatinum group. The diamond crystals react with the silane and hydrogengas to produce the crystal layer.

The epitaxial metastable crystal layer on the diamond, SiC or cubicboron nitride will react when mixed with a suitable metal powder underpressure at liquid or eutectic temperatures to produce a metallurgicalbond with the metal.

The treated diamond, SiC or cubic boron nitride can be used formanufacturing abrasive tools, drawing dies, cutting tools, etc., by hotpress or sintering. It is also possible to manufacture rotary tools byelectroplating. Preferably the electroplating is performed using asquare wave current and a catalyst which will catalyze the reaction ofthe metastable crystal layer with metal which deposited on thesubstrate.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1(A) and 1(B) are an X-ray map of diamonds treated in accordancewith the invention;

FIG. 2 is a photomicrograph of steel coated with a tungsten carbidecloth mixed with the treated diamonds and which was used in a dryabrasion test;

FIG. 3 is a photomicrograph of a section of the coated steel specimen ofFIG. 2 after the abrasion test;

FIGS. 4(A), 4(B), 4(C) and 4(D) are photomicrograph of a cross-sectionof the coating of FIG. 2;

FIG. 5 is is a photomicrograph of a Ti-6Al-4V substrate coated with aNiCoB alloy and treated diamonds from a chemical plasma depositionprocedure;

FIGS. 6 and 7 are photomicrographs of treated diamonds bonded to NiCoBalloy in a electrodeposition procedure, with approximately 80% of thediamond protruding from the alloy;

FIG. 8 is a photomicrograph showing the treated diamonds and the NiCoBalloy after electrolytic deposition on a dental bur, with approximately30% of the diamond protruding from the alloy; and

FIGS. 9 and 10 are photomicrographs showing bonding between a NiCoBalloy to a substrate and to the treated diamonds.

FIG. 11 is a photomicrograph showing diamonds bonded to a substrate inaccordance with Example 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Diamonds are, of course, crystalline carbon. Their structure is aninterlaced face centered cubic crystal from which tetrahedral bonding isgenerated by covalent bonds.

Every carbon atom has four covalent bonds with the exception of theatoms at the surface of the crystal. These atoms have only threecovalent bonds leaving one bonding site per atom unfulfilled. The oxideof a diamond is carbon dioxide, a gas at normal conditions oftemperature and pressure. Therefore, carbon dioxide cannot fulfill thesurface bonding requirements of diamond. Given these conditions,airborne dust particles and oil in the average home are sufficient tocoat the surface of the diamond and help to satisfy its need for a bond.Under some conditions the unfulfilled covalent bond will have an extremeaffinity for hydrocarbons and/or silicons. This affinity is used, as isdescribed below, for the epitaxial growth of a metastable crystal layeron the diamond which will allow the diamond to bond to metallicsubstrates.

To grow the metastable layer, the diamond surface must be clear of anyimpurities, such as the above-mentioned dust and oil. The diamond isinitially cleaned with solvents such as trichloroethylene orethyl-methyl-ketone, and then cleaned with nitric, sulfuric andhydrofluoric acids. The diamond surface is then etched with the vaporsof hydrofluoric acid and nitrogen.

After these preliminary treatments, the diamond is placed in a tungstencarbide crucible which is then inserted in a plasma reactor wherein thediamond is treated. The crucible is plated with a catalyst, preferablyplatinum. The crucible is connected at one end to a positive pole and atthe other end to a negative pole of a DC power source. The size of thecrucible should be large enough to contain the amount of diamonddesired. It should also be proportional to the size of the plasmareactor. The reactor is preferably in a horizontal position.

Before treating the diamonds, the reactor and diamonds are purged andcleaned. This is done by first purging the reactor with nitrogen. Thereactor is then raised to 750° C. for annealing at a pressure of onetorr. The diamonds are then washed in a hydrogen atmosphere at 900° C.for 24 hours at a pressure of 1×10⁻³ Torr. The reactor is then purgedwith nitrogen and cooled for about 180 to 240 minutes.

After the purging and cleaning, the metastable crystal layer is grown byreacting silane with hydrogen in the presence of a catalyst (preferablyplatinum) at the pressure of 1×10⁻³ Torr and temperature in the range ofabout 800° C. to about 1050° C. The silane is preferably adialkyldichlorosilane, preferably dimethyldichlorosilane ordiethyldichlorosilane. The reaction of the silane and hydrogendisassociates the silane to produce hydrocarbons, silicon, and HCl inaccordance with the following reaction: ##STR1##

The atomic silicon liberated in this reaction, when contacting thesurface of the diamonds, orients itself in the exact configuration ofthe diamonds and is deposited thereon. Because of the environmentsurrounding the diamonds as well as the temperature conditions employed,the silicon reacts with the carbon (diamond) to produce silicon carbidemetastable crystal layer on the diamond surface. The silicon carbide isformed in accordance with the following reaction: ##STR2##

As in all processes the reaction conditions are extremely important toan efficient operation.

The desirable temperature for disassociation of the silane in order toliberate silicon is about 800° C. to about 1050° C. This temperatureassures that no elemental carbon is formed from the diamonds (i.e. thediamond is not depleted) before the silicon bonds at the empty bondingsites to fulfill the bonding requirements. The pressure is preferably1×10⁻³ Torr.

The environment surrounding the diamonds during the growth of ametastable crystal layer consists of at least 96% hydrogen and about 4%or less silane, by volume. Of course, the silane is the source ofsilicon, but the hydrogen gas is another important component of theenvironment surrounding the diamonds. The purpose of the hydrogen gas isto react with the Silane resulting in the breakdown that will liberatethe silicon. The hydrogen gas, in the presence of the catalyst and undertemperature conditions of between 800° C. and 1050° C., will ionize andreact with the silane to form hydrocarbon gas and hydrochloride gas andto liberate the silicon. The liberated silicon will then react with thediamonds, fulfilling the surface bonding sites and will grow on thesurface of the diamonds. The silicon reacts with the diamond to formSiC. The metastable crystal layer will react later with any suitablemetal powder under high pressure at liquid or eutectic temperatures ofthe metal, allowing a metallurgical bond with the metal. The bond shouldreact in an aqueous medium, e.g. suitable plating solution where aheterogeneous catalyst of group VIII of the Periodic Table is present toplate a substrate.

The catalyst plated tungsten carbide crucible acts as a secondary sourceof heat, independent of the source of power of the reactor during thereaction. This additional source of heat helps sustain the temperatureof the solid crystals at the same level as the gas environment.

EXAMPLE 1

One thousand carats of diamonds, mesh 100/120, were deposited in thecrucible. After cleaning with solvents and acids as above, the cruciblecontaining the diamonds was placed inside of the chemical plasmadeposition reactor. The reactor was closed, and the diamonds werecleaned with hydrogen for 24 hours as described above, leaving thesurface atomic layer free at the empty bonding site.

The reactor was purged with nitrogen and annealed at 650° C. for 30minutes, creating a gaseous atmosphere. The atmosphere included byvolume, 99% hydrogen gas and 1% dimethyldichlorosilane (DMDCS) gas. TheDMDCS gas is produced by induction heating DMDCS at 69°-72° C. at whichpoint it evaporates to produce gas. The reactor temperature was thenraised to, and maintained at, 875° C. The reactor pressure wasmaintained at 1×10⁻³ Torr.

The reaction was performed in the presence of the catalyst which linedthe crucible containing the diamonds.

After 48 hours the chemical plasma deposition reactor was cooled forfour hours and evacuated.

When the reactor was opened, the crucible containing the 1000 carats ofdiamonds was examined and the diamonds were removed. The diamondsappeared a little darker then before the treatment, but were stilltransparent. The total weight was 1001 carats (100.2 grams). In otherwords the metastable crystal layer growth was 0.1% by weight.

The treated diamonds were then tested.

EXAMPLE 2

A small sample of the treated diamonds were first examined using theSEM-EDS unit to determine the approximate concentration of the elementsheavier than Sodium. Silicon was detected on the diamonds; no otherelements were detected to any appreciable degree. FIGS. 1 and 4 presentsan X-ray map of elements encountered in the sample. It is clear that thetreated diamonds had silicon and carbon associated with the surfacewhich partially diffused into the interior of the diamonds.

Two 1×3 inch abrasion test samples were made of 1018 steel were coveredwith a tungsten carbide cloth with treated diamonds thereon. The samplescoated with the cloth and diamonds were braze-infiltrated withNicrobraz-120, a nickel-base brazing filler having 70-76% Ni, 13-15% Cr,4-5% Fe, 3-5% Si, 2.8-4% B, and 0.6-0.9% C, available from Wall ColmonoyCorporation in Detroit, Mich., in a dry hydrogen atmosphere at 2150° F.(1177° C.) and 1 Torr for five minutes. A brazing filler of the samecomposition is available from the Metco division of Perkin Elmer underthe trade name Metco-15E.

The two coated steel specimens were surface-ground using a water-cooleddiamond-rimmed wheel 8" in diameter and 0.5" in width. The wheel wasoperated at 2300 RPM; the table feed was manually controlled. In sharpcontrast to the regular grinding of the tungsten carbide cloth coating,the tungsten carbide cloth mixed with the treated diamonds was clearlymore difficult to finish. In fact the grinding wheel was finished,rather then the sample, showing that the diamond covered steel was veryabrasive. In order to conserve the grinding wheel, a section of only1.5-2.0 inches was finished. (FIG. 2).

The specimens were then tested using procedure of the ASTM G-65 standardon dry sand rubber abrasion testing. Both samples tended to deeplygroove the rubber rim of the steel wheel. In both instances the diamondparticles were left standing proud.

The abrasion tested samples were sectioned and prepared formetallographic examination. Representative photomicrographs are given inFIG. 3. In general, the microstructure showed excellent integrity at theinterface between the diamond and tungsten carbide coating and the 1018steel substrate.

In order to confirm the chemistry of the diamonds, a qualitativemicroanalysis was performed on the polished cross-section of thecoating. An examination with a microprobe showed that the diamondparticles were rich in carbon. The silicon, which was associated withthe diamond surface, appeared to have diffused into the diamond matrix.(FIGS. 4A-4D)

EXAMPLE 3

A group of 25 tip-tests made of titanium (90%), aluminum (6%) andvanadium (4%) (Ti-6Al-4V) was placed in a special device to plate thetips with an alloy and the treated diamonds by chemical plasmadeposition. The tip-tests were activated with a solution of iodine andmethanol. The device had a shape that permitted intimate contact of thetip-tests with the treated diamonds. The device also allowed the piecesto fit in the crucible.

Once the device was adequately prepared, it was placed in the reactionchamber of the chemical plasma deposition reactor which was then closed.First the reactor containing the device with the tip-test pieces anddiamonds was purged with nitrogen. The reactor temperature was raised to225° C. and the tip-tests and diamonds were annealed for 30 minutes at apressure of one Torr. The reactor was purged again with hydrogen gas.The temperature was then raised to 285° C. and a line connected to aheated bottle containing nickel and cobalt salts and boron was opened.The heated bottle contained about 1 mole NiSO₄, 0.25 mole NiCl₂, 0.125mole CoSO₄, and 0.0125 mole B. Hydrogen gas was used as a carrier forthe nickel, cobalt, and boron salts. The reaction took place at apressure of 1×10⁻³ Torr. The reactor atmosphere was 96% H₂ and 4% metalcompounds. After 3.5 hours, the reactor was purged with nitrogen andcooled for about two hours.

The reactor was opened and the device containing the tip-tests and thetreated diamonds was removed. The excess diamonds were carefully removedso that the condition of the tip-tests now coated with the bondablediamonds and the Ni-Co-B alloy could be evaluated. The first opticalmicroscopic examination showed a single layer of diamonds with aprotrusion of about 30% of the average size of the diameter of thediamond crystals.

One of the tip-tests was cut and prepared for electron-microscopicexamination It was found that the Ni-Co-B alloy was diffused into theTi-6Al-4V and the diamonds were perfectly bonded to the Ni-Co-B, forminga single unit (FIG. 5).

EXAMPLE 4

A device was prepared which permitted 100 pieces of specially shapeddental burs to be connected to a source of power for electrolyticplating. The device also contained an adequate quantity of diamonds toallow intimate contact with the metal substrate; in this case the shapeddental burs.

The dental burs and treated diamonds were lowered into a plating bath toelectrolytically plate the burs with an alloy coating and the treateddiamonds of Example 1. An electrolytic bath was used containing nickelmetal (54%), cobalt metal (44%), boron (2%) in the presence of acatalyst, preferably solid palladium. Nickel anodes were used. Thesource of power was a pulse square wave current having a 30% duty cycleand a frequency of 1000 Hz, the temperature of the solution was 66° C.,and the Ph was 3.8. The electrolytic plating process preferably isperformed as described in my co-pending application Ser. No. 594,570,filed on Oct. 9, 1990 and which is incorporated herein by reference.

The electrolytic process was done in about 90 minutes at an average of0.570 amperes. When the operation was completed, the device containingthe metal substrate and the diamonds was removed. After removing theexcess diamonds, the dental burs were cleaned with distilled water anddisconnected from the device.

The amount of metal deposited had been planned to have 80% of theaverage diameter of the diamonds to extend beyond the metal to test ifthe diamonds were bonded to the stainless steel substrate. Thedeposition time can be determined from Faraday's law. Microscopicexamination showed that the calculation of the deposited metal wascorrect. The metal was brilliant and beautiful. The diamonds wereperfectly bonded to the Ni-Co-B alloy formed in the aqueous solution.FIGS. 6 and 7 show the disposition of the diamonds with 80% of theiraverage diameter extending beyond the metal alloy.

The diamonds were not encapsulated, like a peanut, by the depositedmetal, but were bonded in the strict sense of the word to the metal.(FIGS. 5, 9, and 10).

EXAMPLE 5

The same electrolytic bath was used as in EXAMPLE 4, with the object ofproving the control of metal deposition on a substrate with the shape ofa cylindrical dental bur. A device was prepared which could be at thesame time a connector and a container of diamonds. The calculations weremade so that the alloy would cover 70% of the average diameter of thecrystals.

The solution was prepared at the temperature of 66° C. at 3.8 Ph andwith a metal concentration of 54% Ni, 44% Co, 2% B. The source of powerwas set at 1000 Hz; 0.3 ms T_(ON) and 0.7 ms T_(OFF).

The run was divided into three steps. First, the substrate wayelectrolytically plated with a layer of Ni-Co-B alloy. The averagesubstrate was immersed in the plating bath. The current used for thecoating was set at 0.590 amps for 12 minutes, 52 seconds for a total of7.60 amps min. This produced a metastable layer of the alloy on thesubstrate.

Second, the coated substrate was placed in intimate contact with thetreated diamonds. An average current of 0.140 amps for 43 minutes, 21sec. for a total of 6.07 amps min. was passed through the substrate.This bonded the diamond to the metal. The silicon which was placed onthe diamond diffused into the alloy to bond the diamond to the alloywhich was coated on the substrate.

Third, more NiCoB alloy was plated around the diamond. The alloy,however, is not deposited on the diamond, rather, the original layer ofalloy grows around the diamond and bonds thereto. (FIG. 11). The averagecurrent used was set at 0.300 amps for 55 min., 24 sec. for a total of16.62 amps min.

After 1 hour, 51 minutes, 37 seconds, which was the total time of therun, the device containing the dental burs and the excess diamonds wasremoved. After cleaning with distilled water, the dental burs wereexamined. The dental burs were found to have a single layer of diamonds,perfectly distributed. FIG. 7 shows the protrusion of about 30% of thecrystals, as was calculated.

One of the dental burs was cut and prepared for metallurgicalexamination. The X-ray (FIGS. 9 and 10) showed perfect bonding of thedeposited metal to the substrate and bonding between the deposited metaland the diamonds.

The forgoing is set forth for illustrative purposes and is not meant tobe limiting. It will be understood that various modifications of thedisclosed ranges of the present invention may be made. Numerousvariations, within the scope of the appended claims.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent is:
 1. A method of treating diamond particlesto enable the diamonds to bond to a metal comprising forming ametastable layer of silicon carbide on said diamond particles, byreacting silicon with diamond carbon to form said silicon carbide at atemperature below 1050° C. in the presence of a catalyst.
 2. The methodof claim 1 wherein said metastable layer forming step is performed bychemical plasma deposition.
 3. The method of claim 1 wherein saidmetastable layer forming step includes:placing said diamond particles ina reactor; charging said reactor with a silane gas and hydrogen gas;reacting said silane and hydrogen at a temperature of between 800° C.and 1050° C. and 1×10⁻³ Torr to produce silicon; and reacting saidsilicon with said diamond.
 4. The method of claim 1 further including astep of cleaning the diamond prior to said metastable layer forming stepcomprising:purging said reactor with nitrogen after said diamondparticles have been placed therein; annealing at about 750° C. and oneTorr; soaking in a hydrogen atmosphere for about 24 hours at 1×10⁻³Torr; purging with nitrogen; and cooling for 180 min-240 min.
 5. Themethod of claim 4 further including a prior step of cleaning saiddiamond before said step of placing said diamond in said reactorcomprising washing said diamond with a solvent, washing said diamondwith an acid, and etching said diamond with acid vapor in the presenceof nitrogen.
 6. A method of depositing diamond particles on a substrate,said method comprising treating said diamond particles at a temperaturebelow 1050° C. in the presence of a catalyst to form a metastablesilicon carbide layer on said diamond particles; depositing a metalalloy on said substrate, said alloy being bonded by a polar-covalentbond to said substrate as deposited; and metallurgically bonding saidtreated diamond particles to said metal alloy.
 7. The method of claim 6wherein said depositing step includes electrolytically depositing saidalloy on said substrate
 8. The method of claim 7 wherein said step ofelectrolytically depositing step includes:placing said substrate inintimate contact with said diamond particles; lowering said substrateand diamond particles into a plating bath, said bath being at about 66°C. and a pH of about 3.8; and running a pulse wave current through saidplating bath whereby said silicon difuses into said alloy and saiddiamond bonds to said alloy.
 9. The method of claim 7 further includinga step of growing said alloy around said diamond.
 10. The method ofclaim 9, wherein said growing step includes electrolytically depositingmore of said alloy around said diamonds, said further alloy beingdeposited on said first coating of said alloy.
 11. The method of claim 6where said depositing step includes depositing by chemical plasmadeposition.
 12. The method of claim 11 wherein said depositing stepincludes:placing said substrate in intimate contact with said diamondparticles; placing said substrate and diamond particles in a chemicalplasma deposition reaction chamber; purging said reactor chamber withhydrogen; charging said reaction chamber with metal salts; andmaintaining said reaction chamber at about 285° C. and 1×10⁻³ Torr forabout 3.5 hours.
 13. The method of claim 12 further including a step ofcleaning the diamond prior to said depositing step comprising:purgingsaid reactor with nitrogen after said diamond particles have been placedtherein; and annealing at about 225° C. and one Torr for about thirtyminutes.
 14. A method of treating diamond particles to enable thediamonds to bond to a metal comprising depositing a metastable layer ofsilicon carbide on said diamond particles, wherein silicon bonds withdiamond carbon to form said silicon carbide and including a step ofpre-cleaning said diamond particles to remove impurities from thesurface of said diamond particles to free up outer bonding sites ofcarbon atoms at the surfaces of said diamond particles, said depositingstep including a step of reacting a silicon-containing compound toproduce silicon, and reacting said silicon with said diamond, saidreacting steps being carried out at a temperature below 1050° C. in thepresence of a catalyst.
 15. The method of claim 14 wherein said step ofproducing silicon is carried out between 800° C. and 1050° C. atsubatmospheric pressure in the presence of said diamond and in thepresence of a catalyst.